Oh, stinky pigs!
Well, it's been hot and sticky and I've found my boars need to be cleaned out more than normal or the living room starts to smell like a barn. So, it could just be normal "ripe" wee smell.
However, when a boar is feeling a bit, um "fruity," they I think their wee tends to have a more, um "manly" odour, iyswim. It may be that Big Pig is getting in the mood, even without the opportunity to do anything about it.
If he's not showing any signs of infection (squeeking or hunkering when weeing, blood in urine - not just urine that's dark and a bit reddish or white when it dries - what I mean is "frank" blood on the bedding or papers,) then it's probably not that. But, you can get urinalysis testing strips on the interwebs to test a bit and the correct values can be found on the Guinea Lynx site I think.
(No, you don't have to give him a little pot to "give a sample" into :) - I tend to put them in a plastic box until they do a wee, then dip the strip in - not sterile, but it will show up blood or protein, which could be signs of problems.)
More water, yes, more water may help. Give him some in a syringe as well to "top up" the levels. Some pigs are big drinkers, some aren't. That's just the piggie way!
Failing that, have you thought of a plug in? 